EP1752746A1 - Electronic weighing device comprising a coupling assembly for a calibrating weight. - Google Patents

Abstract

Calibration weight device (102) comprises a transfer mechanism having a polystable positioning element (115) whose first stable state defines the calibration position and whose second stable state defines the resting position of the transfer mechanism. The drive of the device is an actuator (118) to which is fed energy only in the moving phase of the transfer mechanism. An independent claim is also included for a method for testing and defining a calibration weight device. Preferred Features: Energy in the form of energy impulses is fed to the actuator. The positioning element is a tristable positioning element with a first stable intermediate position arranged between the calibration position and the resting position.

Description

The invention relates to a calibration weight arrangement for a gravimetric measuring device or an electronic balance, and in particular to a transfer mechanism for a calibration weight arrangement.

Electronic scales are often calibrated using an internal calibration weight. For calibration, a calibration weight having a defined mass is brought into force contact with the force transmission device arranged in a load cell of a balance or with the load receiving area of the load cell, and then a reference value is determined. Based on this reference value, further weighing parameters of the balance can be adjusted. After successful calibration, the contact between the calibration weight and the power transmission device or the load receiving area is released again and the calibration weight locked in a rest position. The calibration weight is thereby moved by a transfer mechanism from a rest position to a calibration position and back. In the calibration position, the calibration weight is in force contact with the load cell or with the load receiving area; There is no force contact in the rest position. In many scales, the Kalibriergewichtsanordnung and the load cell are arranged one behind the other, as in the EP 0 955 530 A1 is disclosed.

There are various transfer mechanisms for moving a calibration weight, which in its rest position usually lies on a support connected to a lifting system.

In the EP 0 468 159 B1 a Kalibriergewichtsanordnung is disclosed with a calibration weight, which moves vertically over pairs horizontally against each other sliding wedges and is brought into force contact with the load cell of the balance. The drive of this transfer mechanism via a spindle connected to the wedges and a motor drive.

A likewise vertical raising or lowering experiences a calibration weight by a in the EP 0 955 530 A1 described device. The weight rests on a support, which is moved by a transfer mechanism with a control disc lifting system or eccentric.

In EP 0 020 030 A1 a Kalibriergewichtsanordnung is disclosed with two independent calibration weights, which are coupled to the same, with the load receiving range of the load cell connected Kalibriergewichtsaufnahme or decoupled from this. The stepped calibration is used to check the calibration device itself. Furthermore, at least one of the calibration weights can also serve to expand the weighing range, as shown in FIG DE 33 30 988 A1 is disclosed.

The mentioned lifting elements are generally driven by small servomotors. A disadvantage of the use of servomotors is that such a comparatively large space in the load cell of the balance required, whereby both the load cell and the balance itself is unnecessarily increased. An improvement of the calibration weight arrangement thus requires in particular an optimization and miniaturization of the drive of the transfer mechanism.

Especially with highly sensitive electronic scales, the weighing result is also influenced and even changed by electrostatic charging and interactions. The servomotors used to drive the transfer mechanisms include electrically non-conductive gear parts which generate frictional electrostatic fields during operation. The resulting electrostatic fields are sufficient to influence the weighing result, especially of highly sensitive scales.

Again in EP 0 020 030 A1 are used as drive solenoids, which are energized during the entire calibration measuring process with electricity. Solenoids thus have the disadvantage, like most small, cost-effective drives, that they have no self-locking properties. Such drives are accurate for operation in a calibration weight arrangement Analytical scales unsuitable because the generated magnetic fields and the heat generated by the long energization time in the coil strongly affect the reference value and the weighing result. Self-locking a drive is its ability to withstand the forces acting on the drive at standstill, so that the drive does not move as a result of these forces.

It is therefore an object of the present invention to provide a calibration weight arrangement which can be used in a small, compact and flexible manner and whose drive neither influences the reference value to be determined nor the weighing result or exerts only the smallest possible influence.

This object is achieved with the features of claim 1. A gravimetric measuring device, in particular a balance, in addition to a load cell with a fixed area and a load receiving area also includes a calibration weight arrangement, wherein at least one calibration weight can be coupled to the load receiving area. If the force measuring cell has a force transmission device for the reduction of the force, the coupling of a calibration weight anywhere in the lever system of the power transmission device is to be understood as a coupling of the calibration weight to the load receiving region. The calibration weight arrangement has at least one calibration weight, a transfer mechanism which comprises at least one restoring element, a lifting system and at least one positioning element and a drive for transferring the calibration weight during a movement phase from a rest position into a calibration position or from the calibration position into the rest position. The at least one positioning element is configured as a polystable positioning element whose first stable state defines the calibration position, and whose second stable state defines the rest position of the transfer mechanism. Of course, the polystable positioning element between the calibration position and the rest position still have other stable positions, for example, to couple a plurality of independent calibration weights with the load receiving area, as in EP 0 020 030 A1 is disclosed. The number of stable positions of the polystable positioning element depends on the calibration procedure. A calibration procedure such as in EP 0 020 030 A1 is proposed requires tristable positioning, in the third stable position, the first of the two calibration weights is placed and at its calibration position, the second calibration weight together with the first calibration weight with the load receiving area in abutment.

Mostly, however, only one calibration weight is used, for which a bistable positioning element is completely sufficient, which merely defines the two positions calibration position and rest position.

Due to the design of the transfer mechanism with a polystable positioning can be used as a drive, a small, cost-effective actuator without self-locking, the power must be supplied to the actuator only during the movement phases of the transfer mechanism. The holding of the transfer mechanism in the calibration position, in the rest position and optionally in other stable positions is effected by the interaction of restoring element and positioning, whereby no force counteracting the return element must be generated by the actuator.

Due to the design of the polystable positioning and the action of the return element of the actuator must be energized only when the guide pin is in certain sections of the guide. This can be done for example in the form of several energy pulses in these sections, but only at the beginning of each movement phase, each with only one energy pulse.

Preferably, an electrical actuator is used and supplied to the actuator energy in the form of current pulses. The actuator, when activated, must be able to overcome the restoring force of the return element.

In the science magazine of the Ruhr-Universität Bochum, RUBIN 2/01, 11th year, winter semester 2001, an article was published under the title "Keep it simple: Kosmak and iLiros", which discloses a compact actuator, which is driven by a shape memory alloy wire , The drive shaft of the drive rotates between two angular positions and back. The two angular positions are also defined by a bistable positioning element or a mechanical flip-flop. Such a shape memory alloy wire or by the English term "shape memory alloy" briefly referred to as SMA wire, requires little space, is not self-locking and therefore offers itself as a drive for the present invention.

The restoring force of the restoring element must be greater than the weight of the calibration weight and the acting in the load direction forces of the transfer mechanism and its frictional resistance. The restoring force of the restoring element holds the transfer mechanism in the calibration position or rest position defined by the positioning element.

This happens, for example, in that a bistable positioning element or mechanical flip-flop has at least one guide piece with a guide groove in the shape of a heart, similar to a cardioid, the shape of which corresponds, for example, to the rest position and the heart shape of the calibration position. At least one guide pin connected to the fixed area engages in this guide groove. The spring force of the restoring element presses the guide pin in the direction of the heart-shaped tip or in the direction of the heart-shaped mold. The heart shape is a common embodiment of such a guide groove. Of course, however, other Führungsnutformen can be used, which allow at least two stable states of the positioning. The design of the individual curve sections depends essentially on the embodiments of the corresponding transfer mechanisms and their sequence of movements. Instead of a guide groove and fittings can be used, the outer or inner contour of the guide groove have a corresponding mode of action. The same applies to the guide pin, whose design depends on the other parts of the positioning.

In principle, a variety of polystable elements can be used for positioning, such as mechanical flip-flops by means of springs, permanent magnets and pneumatic and hydraulic solutions.

So that the guide pin in the guide groove of a polystable positioning element also always maintains the correct direction of rotation and does not run back the same curve section, means must be provided to prevent a return. Such means may be resilient tongues within the guide groove which, like a switch tongue, block curve sections. Easier is the use of a resilient connection such as a thin-pin bending spring or a Biegegelagers, which is arranged between the lifting system and the polystable positioning, wherein the thin-bending spring or the Biegegelager is then in bending stress neutral state, when the guide pin is between the calibration position and the rest position. Characterized biased in the stable positions of the guide pin relative to the guide piece in a predetermined direction and can continue in accordance with the geometry of the guide groove and the force vectors of the return element and the Dünnstellenbiegefeder resulting force vector, only in one direction. In general, of course, the guide pin with the lifting system and the guide piece to be connected to the fixed area.

However, the polystable positioning can also include a mechanism, as used for example in pens and, for example, in DE 12 69 012 B1 or in FR 431 346 is described. In this case, the positioning element has at least one guide piece in the form of a rotatably mounted roller or sleeve connected to the fixed region of the load cell, wherein the cylinder jacket includes at least one guide groove with the two positions calibration position and rest position, in which engages at least one guide pin connected to the lifting system , Of course, the guide piece in the form of a rotatably mounted roller or sleeve with the lifting system, and the guide pin can be connected to the fixed area.

Preferably, the lifting system has at least one knee joint. The return element and the lifting system are coordinated so that the knee joint already buckles when exposed to a low tensile force on the lifting system, whereby the calibration weight brought into force contact with the load cell becomes. The force of the return element in turn is designed so that it stretches the knee joint when the force on the lifting system decreases.

Depending on the configuration of the transfer mechanism and in particular of the lifting system, different types of return elements can be used. These include various types of springs or other components with similar effects. The return elements are preferably slightly biased in the rest position of the Kalibriergewichtsanordnung. Various types of springs, such as, for example, torsion springs, helical compression springs, tension springs, torsion bar springs or leaf springs can be used. Particularly advantageous in the use of a leg spring is that the restoring force of the spring acts directly on the knee joint and the spring itself can not vibrate due to the mounting or otherwise change the position.

Preferably, two parallel knee joints are used, the connecting axes connect both knee joints accordingly, so that both knee joints move simultaneously and do not inhibit each other or even wedge. One or more knee joints, in turn, may comprise a plurality of mold parts, which are connected to each other directly or via suitable connecting means, or may also be integrally formed. The lifting system, the return element and at least parts of the positioning can also be integrally connected to each other. With appropriate design, the lifting system may include only a single knee joint.

The restoring force of the restoring element is matched to the corresponding transfer mechanism in order to ensure an optimal sequence of the calibration process, ie the contacting and releasing of the contact between the calibration weight and the power transmission device or the load receiving area.

As an actuator without self-locking for a Kalibriergewichtsanordnung with a designed as a knee joint lifting system to offer various drives and in particular linear actuators, such as spindle drives, belt drives, magnetic drives but also linear motors. Especially small and Compact are drives that are at least partially designed from a shape memory alloy. Even a manual actuation of the transfer mechanism is conceivable, wherein, of course, transmission means must be provided in order to transfer the manually applied energy pulse to the transfer mechanism. The actuator can trigger the transfer mechanism, for example, by implementing the force via at least one roller or a lever.

However, the use of a polystable positioning element involves the problem that the current position of the calibration weight arrangement is not known each time the gravimetric instrument is put into operation. This may well change as a result of environmental effects such as shock, even if the gravimetric meter is turned off. This can only be prevented if the mechanism is provided with expensive locking measures. It is simpler and more cost-effective if, each time the gravimetric measuring device is put into operation or periodically, the current state of the calibration weight arrangement is checked and a defined state, for example the rest position, is approached. For examining and defining the state of the calibration weight arrangement with a polystable positioning element, for example, the following method can be used.

First, a reference signal value of the load cell is determined and stored this reference signal value with the position number one. Then, each further stable position of the polystable positioning element is traversed until the position of the reference signal value is reached again, wherein a weighing signal value of the load cell is determined in each stable position, and this is stored in the traversed order with position numbers. The weighing signal values and the reference signal value are then compared with each other, whereby the smallest signal value and its position difference relative to the position of the reference value are determined. Starting from the position of the reference value, the actuator is then supplied with so much energy pulses according to the determined position difference until the position with the smallest signal value is reached, which corresponds to the rest position.

If a bistable positioning element is used in the calibration weight arrangement, the method is simplified as follows:

Again, a reference signal value of the load cell is first determined and stored. Thereafter, the actuator is supplied with an energy pulse and a weighing signal value of the load cell is determined, the reference value compared with the weighing signal value and the actuator supplied with a further energy pulse, if the weighing signal value is greater than the reference signal value.

If a reference value has already been stored at the factory, for example the weighing signal value with the calibration weight arrangement in unloaded load position, the determination of a reference value is unnecessary and the actuator is supplied with energy pulses until the weighing signal value of the load cell corresponds to the reference value, but at most only so many how stable positions exist.

Fig. 1

eine schematische, vereinfachte Seitenansicht einer Kraftmesszelle einer elektronischen Waage mit verlängertem Kalibriergewichtsarm und einer neben der Kraftmesszelle angeordneten Kalibriergewichtsanordnung mit einem Kalibriergewicht, wobei in Figur 1a das Kalibriergewicht in seiner Ruheposition und in Figur 1 b das Kalibriergewicht in seiner Kalibrierposition dargestellt ist;

Fig. 2

eine schematische, vereinfachte Seitenansicht einer Kalibriergewichtsanordnung mit einem Kniegelenk, einem als Draht ausgestalteten Aktuator aus einer Formgedächtnislegierung und einem polystabilen Positionierelement, wobei in Figur 2a die Kalibriergewichtsanordnung in Ruheposition, und in Figur 2b die Kalibriergewichtsanordnung in Kalibrierposition dargestellt ist;

Fig. 3

eine schematische, vereinfachte Seitenansicht einer Kalibriergewichtsanordnung mit einem Kniegelenk, einem als Draht ausgestalteten Aktuator aus einer Formgedächtnislegierung und einem polystabilen Positionierelement in Form einer drehbar gelagerten Walze, wobei das Kniegelenk zur Erreichung einer geringeren Bauhöhe einen spitzen Winkel zwischen den Kniegelenklaschen aufweist;

Fig. 4

das polystabile Positionierelement in Form einer drehbar gelagerten Walze von Figur 3, wobei die Figuren 4a bis 4d verschiedene Positionen des Positionierelements darstellen;

Fig. 5

eine Seitenansicht eines einstückig ausgeformten, in der Ruheposition dargestellten Transfermechanismus mit einem integrierten Überlastschutz und einem bistabilen Positionierelement;

Fig. 6

einen Ausschnitt einer Seitenansicht eines einstückig ausgeformten, in der Ruheposition dargestellten Transfermechanismus analog der Figur 5 mit einem integrierten Überlastschutz, wobei der Ausschnitt anstelle des bistabilen Positionierelementes ein tristabiles Positionierelement zeigt.

Various embodiments of the calibration weight arrangement are shown below in the figures. The figures show:

Fig. 1

a schematic, simplified side view of a load cell of an electronic balance with extended Kalibriergewichtsarm and arranged next to the load cell Kalibriergewichtsanordnung with a calibration weight, wherein in Figure 1a, the calibration weight in its rest position and in Figure 1 b the calibration weight is shown in its calibration position;

Fig. 2

a schematic, simplified side view of a Kalibriergewichtsanordnung with a knee joint, designed as a wire actuator of a shape memory alloy and a polystable positioning, wherein in Figure 2a, the Kalibriergewichtsanordnung in rest position, and in Figure 2b, the Kalibriergewichtsanordnung is shown in calibration position;

Fig. 3

a schematic simplified side view of a Kalibriergewichtsanordnung with a knee joint, designed as a wire actuator of a shape memory alloy and a polystable positioning in the form of a rotatably mounted roller, the knee joint to achieve a lower height has an acute angle between the knee brackets;

Fig. 4

the polystable positioning element in the form of a rotatably mounted roller of Figure 3, wherein Figures 4a to 4d represent different positions of the positioning;

Fig. 5

a side view of an integrally formed, shown in the rest position transfer mechanism with an integrated overload protection and a bistable positioning;

Fig. 6

a detail of a side view of an integrally formed, shown in the rest position transfer mechanism analogous to Figure 5 with an integrated overload protection, the cutout instead of the bistable positioning shows a tristable positioning.

To illustrate the known arrangement of a load cell 6 and a calibration weight 2 in a gravimetric instrument 1 or in an electronic balance these are shown in Figure 1 in side view. FIG. 1a shows a calibration weight arrangement 2 in its rest position and FIG. 1b shows a calibration weight arrangement 2 in its calibration position. The load cell 6 has a parallel guide with a fixed portion 3 and a two parallelogrammic link 4 articulated to this load receiving area 5. The fixed area 3 and the calibration weight arrangement 2 are fixed to a base 39, for example the housing bottom of the gravimetric measuring device 1. The load receiving area 5 is connected via the cone 7 with a weighing pan, not shown here, and deflected by loading the same relative to the fixed area 3 vertically in the direction of gravity. A deflection of the load receiving area 5 in the direction of gravity causes a power transmission to a lever mechanism 8, which reduces the force and forwards to a not shown here in detail, mostly electromagnetic force compensation system 11.

The parallel guide 3, 4, 5 and the lever mechanism 8 of the load cell 6 are formed in the substantially cuboid block of material such that its material areas are separated by material-free areas in the form of thin, the block of material perpendicular to its extensive area passing cut lines 12. The cutting lines 12 are preferably produced by means of spark erosion.

The lever 9 of the lever mechanism 8 is provided with through holes on which by means of suitable fastening means 41 a Kalibriergewichtsarm 13 is attached as an extension such that even by means of a calibration weight 14 low mass full load calibration can be performed.

As can be seen in FIG. 1 a, a calibration weight 14 rests on a calibration weight support 21 during a weighing process and is pressed against the side parts of the calibration weight arrangement 2 configured as parking stirrups 16. From this representation, the front side part of the calibration weight arrangement 2 has been removed so that the calibration weight support 21 and, above all, the contact point between the calibration weight 14 and the calibration weight arm 13 can be seen. The same applies to Figure 1 b.

The calibration weight 14 is completely decoupled from the lever mechanism of the load cell 6 in FIG. For a calibration, the calibration weight 14 is lowered onto the calibration weight arm 13 by means of a transfer mechanism, which is here covered by the calibration weight support 21, and thereby brought into force contact with the lever mechanism 8, as shown in FIG. The calibration weight 14 thus completely rests on the calibration weight arm 13 in the calibration position. The transfer mechanism has a lifting system and a drive. The drive is generally arranged next to the calibration weight arrangement 2, relative to the representation in front of or behind the plane of the drawing.

The schematic, simplified side view of a calibration weight arrangement 102 is shown in FIG. 2, FIG. 2a showing the calibration weight arrangement 102 in the rest position and FIG. 2b the calibration weight arrangement 102 in the calibration position. The calibration weight assembly 102 is connected to the fixed portion of the load cell (not shown) via a base 39 and includes the calibration weight 14, a lift system 110, an actuator 118, 119, and a polystable positioning member 115.

The lifting system 110 comprises a linearly guided orthogonal to the base 39 guide rod 123, an articulated arm 125, one end of which is rotatably connected to a, fixed to the base 39 bearing block 140 and a Connecting lug 124, the first end of which is pivotally connected to the end of the guide rod 123 facing the base 39 and the second end engages articulated by means of a pivot bearing 126 in the middle of the articulated arm 125. At the knee joint 117 formed by the articulated arm 125, the spherical plain bearing 126 and the connecting lug 124, a heatable actuator configured as a wire without self-locking 118, 119 of a shape memory alloy acts as part of the drive in the region of the pivot bearing 126. Shape memory alloys are characterized in that they change their physical properties due to a solid phase transition when a phase transition temperature is exceeded. Shape memory alloys are more moldable at temperatures below their phase transition temperature than at temperatures above the phase transition temperature. A temperature increase beyond the phase transition temperature causes, in the case of the configuration as a wire, that this can be shortened and thus exert a force which, for example, acts as a pulling force on the knee joint 117 shown here and thus triggers its movement. The temperature increase can be carried out in a simple manner by applying the wire 118 with current, here indicated by the electrical supply line 119 at one end of the wire. The wire 118 is grounded at the opposite end, which is not visible here.

As the wire shortens, the hinge bearing 126 is displaced, thereby buckling the knee joint 117, resulting in a linear displacement of the guide rod 123 in a direction orthogonal to the base 39. Since at the end remote from the base 39 of the guide rod 123, the Kalibriergewichtsauflage 121 is attached, this undergoes a shift in the direction of the base 39. The resting on the Kalibriergewichtsauflage 121 calibration weight 14 is in this way, for example, half stroke of the lifting system 110 on the Kalibriergewichtsarm 13th applied and completely decoupled from the transfer mechanism. In order to undo this movement course, or to lift the calibration weight 14 again from the calibration weight arm 13, a return element 122 must be arranged in the form of a helical compression spring between the base 39 and the calibration weight pad 121. As soon as the tensile force of the actuator 118 subsides, the knee joint 117 "stretches" as a result of the restoring force of the Return element 122 again and the calibration weight 14 is lifted by the lifting system 110 from Kalibriergewichtsarm 13 and decoupled. In addition, if the actuator 118 has an SMA wire, the reset element 122 also causes the wire, which cools after calibration, to be stretched back to its original length, which requires a force.

In order not to constantly supply power to the actuator 118 during the calibration process to maintain the transfer mechanism in the calibration position, a guide piece 130, which is part of the polystable positioning member 115, is secured to the base 39. The guide piece 130 has a guide groove 131 whose shape substantially corresponds to that of a heart. This polystable positioning element 115 can thus also be referred to as a bistable positioning element 115. The movable part of the positioning element 115, comprising a guide pin 129 and a guide coupling 128, is connected via a thin-point bending spring 127 to the end of the articulated arm 125 facing away from the bearing block 140. The position shown in Figure 2a corresponds to the rest position. The thin-point bending spring 127 is pretensioned, exerts a moment M + clockwise on the guide coupling 128 and thus presses the guide pin 129 against the edge of the guide groove 131 facing away from the base 39. The shape and position of the guide groove 131 is thus matched to the movement sequence of the articulated arm 125, the guide pin 129 always passes through the guide groove 131 in the counterclockwise direction due to the resultant force vector from the moments of the spring elements 127, 122.

The sequence of movements described below is intended to explain this in more detail. For a better overview, the sections of the guide groove 131 are designated only in Figure 2b. The guide groove 131 has a heart tip 133 which defines the resting position, and a heart cavity 132 which defines the calibration position of the transfer mechanism. The base portion 39 facing away from the groove portion of the guide 131 is as a first portion 134, which is arranged between this portion 134 and Herzkuhle 132 groove portion as the second portion 135, the base 39 facing groove portion as the fourth portion 137 and between this portion 137 and the Herzkuhle 132 arranged groove portion is referred to as third portion 136.

As soon as the knee joint 117 buckles due to the force of the actuator 118, the guide pin 129 slides from the rest position shown in FIG. 2a through the first section 134, since the moment M + generated by the thin-point bending spring 127 or the force vector acting on the guide pin 129 as a result the guide pin 129 presses against the base 39 facing away from flank of the first section 134. In this section 134, between the apex 133 and Herzkuhle 132 of the guide pin 129 reaches the point at which the thin point bending spring 127 reaches a bending stress neutral state. The further the guide pin 129 is moved in the direction of the second section 135 or Herzkuhle 132, the stronger the thin-point bending spring 127 is stretched again, but now exerts a torque M- in the counterclockwise direction. As soon as the second section 135 is reached, the guide pin 129 follows the second section 135 due to the force vector caused by the thin-point bending spring 127 in the direction of the base 39. The power supply to the actuator 118 is reached when a first reversal point 138 which is approximately in the middle of the second section 135 is stopped, and the guide pin 129 slides due to the spring force of the return element 122 in the Herzkuhle 132. The articulated arm 125 is thereby held in a position as shown in Figure 2b, which corresponds to the calibration position. A moment M- of the thin-film bending bearing 127 still acts in the heart cavity 132, so that the guide pin 129 is pressed against the third section 136 and slides through it as soon as the actuator 118 is energized again. The power supply is interrupted as soon as the second reversal point 139 is reached by the guide pin. The restoring element 122 now pulls the guide pin 129 through the second half of the third section 136 and the fourth section 137 in the direction of the apex 133. In the section 137 is due to the geometric conditions again a bending moment reversal in the thin point bending spring 127 instead, so that upon reaching the Heart tip 133 of the force vector on the guide pin 129 again acts in the direction away from the base 39 direction. The articulated arm 125 and thus the calibration weight 14 are as shown in Figure 2a, back to the starting position, which corresponds to the rest position.

The embodiment of a calibration weight coupling 202 shown in FIG. 3 has a lifting system 210 which has essentially the same functional elements as the lifting system 110 from FIG. To achieve a lower overall height, however, the bearing block 240 is fixed above the calibration weight on a carrier 40, which is rigidly connected to the base 39 and at the same time serves as a parking bracket for locking the calibration weight 14. As a result, the knee joint 217 has an acute angle between the connecting strap 224 and the articulated arm 225. The guide rod 223 is linearly guided on the base 39, the calibration weight pad 221 connected to the guide rod 223 is configured analogously to the calibration weight pad 121 in FIG. 2 in order to transfer the calibration weight 14 to the calibration weight arm 13 upon actuation of the lifting system or to take it over again from the calibration weight arm 13 , The return element 222 in the form of a tension spring acts directly on the spherical bearing 226 and thus directly against the tensile force of the actuator 218. The restoring element 222 also pulls the knee joint 217 in rest position against a fixed to the base 39 stop 241. In this position, the connection tab 224 relative to the articulated arm 225 arranged so that by the position of the knee joint 217 acting on the lifting system 210 overloads, caused for example by blows from the outside, are received directly from the stop 241 via the knee joint 217. As a result, the actuator 218 is not destroyed by overloads. Between the actuator 218 and the spherical plain bearing 226, a polystable positioning element 215, also here in a bistable design, is arranged in series with the actuator 218. To clarify the operation of this part is shown in a spatial representation. The serial arrangement is not mandatory; an arrangement parallel to the actuator 218 is also possible. The guide piece 230 in the form of a roller rotatably mounted on a connecting coupling 228 has a guide groove 231 on which surrounds a heart-shaped, raised center contour 249, the level of the heart-shaped surface corresponding to the center contour 249 of the cylinder outer wall. The guide piece 230 is rotatable relative to the connecting coupling 228, but not slidably mounted in the axial direction. Ideally, the entire polystable positioning element 215 is guided linearly, shown schematically in Figure 3 by the bearing 242, in which the guide pin 229 is directly integrated. But guided so the coupling coupling 228 must have a joint 248 or at least elastic be educated. The guide groove 231 is designed so that by the linear displacement of the guide piece 230 relative to the fixed guide pin 229, the guide piece 230 is respectively rotated by means of edge portions 243, 244, 245, 246, 247 of the guide groove 231 in the correct position, so that the guide pin 229 always passes through the guide groove 231 shown in Figure 3 in a clockwise direction. It is important that the guide piece 230 relative to the connecting coupling 228 or the bearing 242 has a certain bearing friction, so that the guide piece 230 each defined by an edge of the guide groove 231 rotation angle until the next flank continues to rotate the guide piece 230. This will not cause any vibration or shock to malfunction. The guide piece 230 shown in Figure 3 is designed for oscillating rotational movements, but there are also rotating guide pieces can be used with a predetermined sense of circulation, as used in the stationery industry, for example in pens. In particular, this embodiment is suitable with oscillating or circumferential guide pieces for applications which require further stable positions between the calibration position and the rest position.

For the purpose of clarifying the mode of operation and the course of movement of the oscillating guide piece 230, the most important positions are shown in FIGS. 4a to 4f. Starting from the rest position 233 shown in FIG. 3, the actuator 218 begins to pull the guide piece 230 through the bearing 242 as a result of the supply of energy. In the first section 234, the guide piece 230 is rotated in the direction D by the contact of the guide pin 229 with the first edge 243, as shown in Figure 4a. As soon as the guide pin 229 reaches the second section 235 and thus the second flank 244, the guide piece 230 rotates in the direction U until the guide pin 299 has reached the first reversal point 238, see FIG. 4b. The power supply to the actuator 218 is now interrupted and the restoring force of the return element 222 pulls the guide piece 230 in the opposite direction through the bearing 242 until the calibration position 232, as shown in Figure 4c, is achieved by the guide pin 229. In this phase, the guide piece 230 rotates further in the direction U as a result of the third flank 245. About the guide pin 229 through the third To move portion 236, power must be supplied to the actuator 218 until the guide pin 229 reaches the second turning point 239. In this case, the guide piece is again rotated by the fourth edge 246 in the direction U and, as shown in Figure 4d, pulled by the actuator 218 through the bearing 242. When the guide pin 229 has reached the second reversal point 239 as in FIG. 4e, the energy supply to the actuator 218 is interrupted again, the direction of movement changes and the restoring element 222 pulls the guide piece 230 back in the direction of rest position 233 through the fourth section 237 is rotated by the action of the guide pin 229 on the fifth edge 247, the guide piece 230 in direction D back to the starting position, see Figure 4f.

Of course, the guide piece 230 could also have a guide groove 131, as shown in FIG. However, the guide piece 230 would then, in order to ensure the correct direction of rotation of the guide pin 229 relative to the guide groove 131, be biased by spring force, for example by a torsion bar spring, in the respective correct direction of rotation.

In addition to the previously presented Kalibriergewichtsanordnungen there is also the possibility of integrally molding the knee joint and other functional parts of the lifting system as the movable part of the positioning, and for example, to combine with a transfer mechanism, similar to that shown in Figures 2 and 3. Such a lifting system 310 of a calibration weight arrangement 302 with an integrally formed knee joint 317 is shown in FIG.

FIG. 5 shows the knee joint 317 in a stretched condition; H. the knee joint 317 is oriented vertically and is in a position near the rest position without the knee joint 317 being pressed against a stop. The contours shown by broken lines indicate that these elements are in a trailing plane of the drawing and would normally be obscured.

The lifting system 310 is in one piece, preferably made of a technical plastic. It consists of three interconnected functional areas. The first functional area 325 has two fastening points 344 for fastening a Stop element 343 and a slot 326. The stop element 343 and the knee joint 317 are firmly connected to each other and can also be realized as a single component. The second functional region 340 is connected to the first functional region 325 firstly via a flexure bearing 324 and secondly via a tension spring as a restoring element 322. The second functional area 340 also has a bearing point 348, the bearing axis 351 of which rotatably supports the second functional area 340 in the extended plane of the lifting system 310 via a bearing plate 349 against a base 39. Also rigidly connected to the bearing plate 349 parallel to the bearing axis 351, a guide pin 352. This guide pin 352 engages in the slot 326 and thus limits the range of movement of the first functional area 325. The translational movement is limited by the length of the slot 326, the rotational Movement via the flexure bearing 324 by the bearing 348 of the second functional area 340. The third functional area 330 is also integrally connected to the first functional area 325 by a thin-point flexure bearing 327. The third functional region 330 has the guide groove 331 already known from FIG. In contrast to FIG. 2, in FIG. 5 the guide groove 331 is moved relative to a guide pin 329 rigidly connected to the base 39. In the illustrated rest position, the Dünnstellenbiegelager 327 exerts a moment M- on the third region 330, so that the guide groove 331 is pushed away from the base 39 against the guide pin 329. The guide pin 329 thus follows the guide groove 331 in a clockwise direction.

As illustrated in FIG. 5, the force application point 360 of the actuator 318 is positioned in the center of the flexure 324. However, this does not mean that the actuator 318 also has to be connected to the flexure bearing 324, it can also be fixed to the abutment element 343 or even to the second functional region 340. The closer the force application point 360 is arranged to the bearing axis 351 or the guide pin 352, the less path the actuator 318 has to apply, but according to the lever law a greater force is required.

The stop element 343 has a corresponding with the bearing axis 351, arcuate slot 353. This serves to protect the bending bearing 324 from overloading, since on the one hand the bending angle of the bending bearing 324 is limited by the arc length of the arcuate slot 353 and on the other hand force peaks Bumps are transmitted in the orthogonal direction to the base 39 directly on the flanks of the arcuate slot 353 on the bearing axis 351.

During the calibration process of the gravimetric measuring device, the actuator 318 exerts a pull directed to the right on the stop element 343 with reference to the drawing. This causes the second portion 340 to deflect by slightly rotating about the bearing axis 351 and buckling the knee joint 317. In addition, the actuator 318 causes the return element 322 to tension and the flexure bearing 324 to flex. As a result, the stop element 343 and the first region 325 of the knee joint 317 pivots to the right and is additionally pulled against the base 39. The calibration weight pad 321 is moved down and the calibration weight is brought into force contact with the load cell.

A shape memory alloy shortens by a certain percentage, e.g. B. shortens a nickel-titanium alloy having a phase transition temperature of about 90 ° C and a Ni content of about 50% by about 4%. The wire 318, however, is flexible and, for example, in the manner shown here via two rollers 380 made of an electrically and thermally non-conductive, sliding technical plastic, such as Teflon, several times deflected. The wire can also be deflected via one or more deflection means such as levers and / or rollers.

In FIG. 6, only the third functional area 430 of a calibration weight arrangement 402, which is otherwise identical to FIG. 5, is shown. Instead of the guide groove 331 from FIG. 5, which has a bistable positioning function as in all the preceding figures, the guide groove 431 of the polystable positioning element 415 has a tristable positioning function. Between the rest position 433 and the calibration position 432 there is a first stable intermediate position 490. In the case of polystable positioning elements with even more intermediate positions, the further stable intermediate positions between the rest position 433 and the calibration position 432 are arranged analogously to the illustrated tristable guide groove 431. The functional sequence of a tristable positioning element or polystable positioning elements with even more intermediate positions does not differ significantly from the functional sequence of bistable solutions. For each intermediate position, only one more energy impulse has to be given to the Actuator supplied to get back to the starting position. In this case, the bending moment reversal in the thin-point bending spring 427 must in each case take place when the guide pin 429 is between the rest position 433 and the calibration position 432 or between the rest position 433 and the first stable intermediate position 490.

In addition to the aforementioned, a shape memory alloy comprehensive actuator without self-locking, in principle, any commercially available drive without self-locking and preferably any linear drive can be used, if this meets the requirements for driving a calibration weight of a gravimetric measuring device, preferably an electronic balance. Known linear drives include u. a. Spindle drives, belt drives, magnetic drives or linear motors. Even manually operable solutions can be used.

As restoring elements, springs such as helical compression springs, tension springs and leaf springs were described in the exemplary embodiments above all. In addition to these explicitly mentioned types of springs, of course, other types of springs or components can be used with comparable effect. Depending on the applied restoring force one or more restoring elements can be used.

The mentioned load cell represents only one of the known types of load cells. The calibration weight arrangement according to the invention can also be used with other load cells.

In Figures 2, 3 and 5, the point of application of the actuator is shown in each case at the knee joint, wherein other points of attack can be realized.

The stop 241 shown in Figure 3 is only exemplified as a kind of housing wall, there are also any other versions with the same effect or function possible, which of course can be used in a suitable manner in an embodiment of Figure 3.

LIST OF REFERENCE NUMBERS

1

Gravimetric measuring instrument, balance

402, 302, 202, 102, 2

calibration weight

3

fixed area

4

parallelogram

5

Load-receiving part

6

Load cell

7

cone

8th

leverage

9

lever

11

Force compensation system

12

intersection

13

calibration weight

14

calibration

16

parking barriers

321, 221, 121, 21

calibration weight

39

Base

40

carrier

41

fastener

310,210, 110

lifting system

415, 215, 115

Polystable positioning element

317,217,117

knee

318, 218, 118

Actuator without self-locking, SMA wire

119

Electrical supply

322, 222, 122

Return element

223, 123

guide rod

224, 124

connecting strap

225, 125

articulated arm

226, 126

Spherical plain bearings

427, 327, 127

Flexure spring

128

guide coupling

429, 329, 229, 129

guide pins

230, 130

guide piece

431, 331, 231, 131

guide

432, 232, 132

Calibration position, Herzkuhle

433, 233, 133

Rest position, heart top

234, 134

first section

235, 135

second subsection

236, 136

third section

237, 137

fourth subsection

238, 138

first reversal point

239, 139

second reversal point

240, 140

bearing block

228

connect switch

243

first flank

244

second flank

245

third flank

246

fourth flank

247

fifth flank

248

joint

249

mid contour

241

attack

242

camp

324

flexure pivot

325

first functional area

326

Long hole

430, 330

third functional area

340

second functional area

343

stop element

344

attachment point

348

depository

349

bearing plate

351

bearing axle

352

guide pin

353

arched slot

360

Force application point

380

role

490

first stable intermediate position

Claims (18)

Calibration weight arrangement (102) for a gravimetric measuring device (1) with a force measuring cell (6) having a fixed area (3) and a load receiving area (5), wherein the calibrating weight arrangement (102) has at least one calibration weight (14) which can be coupled to the load receiving area (5) ) and a transfer mechanism, and the transfer mechanism includes at least one return element (122), a lift system (110) and a drive for transferring the at least one calibration weight (14) during a movement phase from a rest position to a calibration position or from the calibration position to the rest position , characterized in that the transfer mechanism comprises at least one polystable positioning element (115) whose first stable state defines the calibration position (132) and whose second stable state defines the rest position (133) of the transfer mechanism, and that the drive is an actuator without self-locking (118). is which energy is supplied only in the movement phase of the transfer mechanism. Calibration weight arrangement (102) according to claim 1, characterized in that the restoring force of the return element (122) is greater than the maximum weight of the calibration weight (14) or the calibration weights and acting in the load direction forces of the transfer mechanism and its frictional resistances, and that the restoring force of Return element (122) holds the transfer mechanism in the positions defined by the polystable positioning element (115), for example in the calibration position (132) or in the rest position (133). Calibration weight arrangement (102) according to one of claims 1 or 2, characterized in that the actuator (118) energy is supplied in the form of energy pulses. Calibration weight arrangement (102) according to any one of claims 1 to 3, characterized in that at the beginning of each movement phase only one energy pulse to the actuator (118) is supplied, which is sufficient, the calibration weight (14), for example, from the rest position to the calibration position or from the Transfer calibration position to the rest position. Calibration weight arrangement (102) according to one of claims 1 to 4, characterized in that the lifting system (110) comprises at least one knee joint (117). Calibration weight arrangement (102) according to one of claims 1 to 5, characterized in that the polystable positioning element (415) is a tristable positioning element, the first stable intermediate position (490) between the calibration position (432) and the rest position (433) is arranged. Calibration weight arrangement (102) according to one of claims 1 to 5, characterized in that the polystable positioning element (115) is a bistable positioning element. Calibration weight arrangement (102) according to claim 7, characterized in that the bistable positioning element (115) has a guide pin (129) and a guide piece (130) with a guide groove (131), wherein the guide groove (131) has a first section (134), a second subsection (135), the calibration position (132), a third subsection (136), a fourth subsection (137) and the rest position (133) and the actuator (118) energy is supplied only when the guide pin (229 ) passes through the first subsection (134) and the second subsection (135) up to a first reversal point (138), or passes through the third subsection (136) from the calibration position (132) to a second reversal point (139). Calibration weight arrangement (102) according to one of claims 7 or 8, characterized in that the bistable positioning element (115) at least one guide piece (130) with a guide groove (131) in heart shape, whose Heart shaping tip (133) of the rest position (133) and the Herzformkuhle (132) corresponds to the calibration position (132), and at least one, in the guide groove (131) cross, with the fixed portion (3) connected to the guide pin (129). A calibration weight assembly (102) according to any one of claims 1 to 9, characterized in that a thin-point bending spring (127) is disposed between the lifting system (110) and the polystable positioning member (115), the thin-bending spring (127) being in a bending stress neutral condition when the guide pin (129) is between the calibration position (132) and the rest position (133). Calibration weight arrangement (202) according to one of claims 1 to 9, characterized in that the polystable positioning element (215) at least one guide piece (230) in the form of a with the lifting system (210) connected, rotatably mounted roller or sleeve, wherein the cylinder jacket at least a guide groove (231) with at least the two positions calibration position (132) and rest position (133), in which guide groove (231) at least one with the fixed portion (3) connected to the guide pin (229) engages. Calibration weight arrangement (102) according to one of claims 1 to 11, characterized in that the restoring element (122) is a leg spring, a torsion bar spring, a leaf spring, a helical compression spring or a tension spring. Calibration weight arrangement (102) according to one of claims 1 to 12, characterized in that the at least one restoring element (122), the lifting system (110) and the polystable positioning element (115) comprises at least three molded parts, which are connected to each other directly or via suitable connecting means , Calibration weight arrangement (302) according to one of claims 1 to 12, characterized in that the at least one restoring element (322), the lifting system (310) and at least a part of the polystable positioning element (330) is integrally formed. Kalibriergewichtsanordnung (102) according to any one of claims 1 to 14, characterized in that the actuator without self-locking (118) is a linear drive, for example a linear motor, a spindle drive, a belt drive, a magnetic drive, a cooperating with a heater wire from a Shape memory alloy or a manually operated device is. Calibration weight arrangement (302) according to one of claims 1 to 15, characterized in that the actuator without self-locking (118) via at least one roller (380) or at least one lever acts on the transfer mechanism. Method for checking and defining the state of a calibration weight arrangement (102) having a polystable positioning element according to one of Claims 1 to 16, characterized in that a. a reference signal value of the load cell is determined and this reference signal value is stored with the position number one, b. each further stable position of the polystable positioning element is traversed until the position of the reference signal value is reached again, whereby in each case a weighing signal value of the load cell (6) is determined in each stable position, and this is stored in the sequential order with position numbers, c. the weighing signal values and the reference signal value are compared with one another, wherein the smallest signal value is determined, and its position is determined relative to the position of the reference value, d. starting from the position of the reference value, go through the stable positions of the polystable positioning element until the position with the smallest signal value is reached. Method for checking and defining the state of a calibration weight arrangement (102) having a bistable positioning element according to one of Claims 7 to 16, characterized in that a. a reference signal value of the load cell is determined and stored, b. the actuator is supplied with an energy pulse, c. a weighing signal value of the load cell is determined, d. the reference value is compared with the weighing signal value, e. the actuator is supplied with a further energy pulse, if the weighing signal value is greater than the reference signal value.

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